1. Field of the Invention
The present invention relates to a surface treatment method, a manufacturing method of a semiconductor device, and a manufacturing method of a capacitive element, and more particularly, relates to a manufacturing method of a capacitive element and a manufacturing method of a MOS transistor, a CCD, a TFT, an SOI substrate, an inkjet head, and the like.
2. Description of the Related Art
A semiconductor device is manufactured by sequentially performing various treatment processes for a substrate such as silicon, sapphire, or glass. The treatment processes mentioned above include, for example, cleaning, oxidation, thin-film formation, dopant doping, and etching.
Treatment apparatuses used for various treatment processes are disposed in a clean room, and all the treatment processes are performed in the clean room. During the treatment processes, a semiconductor substrate is exposed to a clean room atmosphere when it is transferred from one process to the following process. In general, when a solid material is exposed to a clean-room atmosphere, moisture therein simultaneously adsorbs on surfaces of the solid material. Moisture (adsorption moisture) which adsorbs on a semiconductor-surface causes, for example, the following adverse influences (1) to (4).
(1) Adsorption moisture itself desorbs in a subsequent step in the form of water vapor and exists as an impurity in the process atmosphere.
(2) Adsorption moisture which adsorbs on a silicon substrate forms a native oxide film thereon when oxygen is present in that atmosphere. For example, when a silicon nitride film is formed on the substrate, the native oxide film thus formed has an adverse influence on the control of quality and uniformity of the film to be grown. In addition, when the above native oxide film is present in the vicinity of a transistor gate, the threshold value and the breakdown voltage of the transistor are varied. Furthermore, on a capacitor electrode of a semiconductor device, electric charges are liable not to be stored.
(3) In a wiring process of a semiconductor device, in order to prevent spikes due to the formation of tungsten silicide, a TiN (titanium nitride) film is formed before a tungsten (W) film is formed. However, when adsorption moisture is present on a semiconductor substrate surface used as an underlying layer, the adhesion of the TiN film is degraded.
(4) When oxidation occurs at connection portions of metal wires of a semiconductor device due to the presence of adsorption moisture, a metal oxide is formed, and as a result, conduction between the metal wires may be blocked, or the connection resistance may be increased in some cases.
As described above, since adsorption moisture has caused various adverse influences, it is required to remove moisture present on a semiconductor substrate surface in every process.
Accordingly, a method has been performed in which a substrate with moisture adsorbed thereon is heated to a high temperature, such as approximately 300° C., to remove the moisture. In addition, a method of irradiation of a noble gas or a hydrogen active species has also been proposed (see Japanese Patent Laid-Open No. 11-260913).
In addition, a method has also been proposed in which moisture is removed by using a water-decomposing gas, that is, a gas reactive with water (see Japanese Patent Laid-Open No. 5-213604).
Furthermore, a method has also been proposed in which a water-soluble gas, that is, a gas having water absorbing properties, is brought into contact with a substrate surface to remove moisture (see Japanese Patent Laid-Open No. 9-106974). In this method, as a gas having water-absorbing properties, for example, hydrogen chloride, hydrogen bromide, and ammonia may be mentioned.
However, the moisture removal by heating and the techniques described in the above cited literatures have various problems to be solved.
For example, according to the above-described techniques, only adsorption moisture present on the topmost surface of a semiconductor substrate can be removed, and in addition, when the semiconductor substrate is again exposed to the atmosphere, a predetermined amount of moisture again adsorbs on the surface of the semiconductor substrate. In particular, it is difficult to prevent re-adsorption of moisture released from the rear surface of the substrate, the moisture being difficult to remove by moisture removal treatment.
In addition, when a water-decomposing gas or a gas having water absorbing properties is used, special treatment and consideration are required for plumbing materials and safety measures. In other words, since these gases have strong toxicity, acidity, or alkalinity, the handling thereof must be performed in a specific manner, and as a result, the increase in facility cost may occur in some cases.
Furthermore, hydrogen chloride, hydrogen bromide, and ammonium gases are strongly corrosive, and depending on a surface material of an object (semiconductor substrate), the surface thereof may be etched in some cases.
In the case of a thin film transistor (TFT), as the surface area of a substrate is increased, the distortion thereof is also increased when adsorption moisture is removed by heating as described above. In addition, when the heating temperature is decreased, it will take a longer time to remove adsorption moisture.
When adsorption moisture on a semiconductor substrate is removed by heat treatment at a high temperature, the profile of impurities is changed, and as a result, it becomes difficult to obtain a predetermined device performance. That is, an impurity such as arsenic (As) or phosphorous (P) forming an n+ layer or boron (B) forming a p+ layer is unfavorably diffused by heat.
Incidentally, as a technique used for forming a gate insulating film of a transistor, there has been a nitridation treatment of a substrate surface (see Japanese Patent Laid-Open No. 11-40397).
In a state-of-the-art transistor, it has been desired that a thin film nitride having a desired thickness be formed on the surface of a semiconductor substrate.
However, since nitridation does not proceed as expected, it has been difficult to obtain a nitride film having a desired thickness. In addition, by the nitridation treatment, the properties of the semiconductor substrate were changed in some cases.
The difficulties of forming the nitride film and the changes in properties of the object described above are problems to be solved by a general surface treatment method used not only for semiconductor device applications but also for other applications.